64 PALAEONTOLOGY OF KENTUCKY. 



Pentamems ventricosus. Km- 



Plate XXXIII., figures 12, 13 and 14. 



Pentamerus ventricosus, Hall. Geol. Kep. Prog. Wis., p. 2 1860. 

 Pent. (Pentamerella) ventricosus, Hall. 20th Keg. Kep., p. 3741868. 

 Pent. (Pentamerella) ventricosus, Hall. Ohio Pal., Vol. II., p. 1381875. 



Shell of medium size, globose ; width and length about equal, sometimes a 

 little wider than long ; hinge-line short, and cardinal extremities rounded. 

 Ventral valve greatly more convex than the dorsal, with a very prominent 

 umbo, and a strongly incurved beak ; the middle of the valve marked by a 

 broad, moderately deep sinus, extending from beak to base, where it forms a 

 basal extension, deflecting upwards to meet a mesial indentation in the dorsal 

 valve. Dorsal valve most prominent at the umbo, from where it runs in a 

 straight line along the summit of the mesial fold to the front ; on both sides of 

 the mesial elevation there is a marked depression, formed by the mesial fold 

 and the markedly upwards turned lateral margins ; beak small and strongly 

 incurved into the opposite valve. 



Surface of the shell is marked by concentric undulations of growth, which, 

 according to Prof. Hall's statement, are visible on the internal casts, but which 

 the specimens in my possession, being casts of the interior, do not show. In 

 my shells the surface is entirely smooth. Medium septum of the ventral valve 

 is very short. This species is easily recognized by its strong umbo and its 

 trilobed appearance in a front view. It differs from the ordinary forms of 

 Pentamerus in having the middle of its dorsal valve elevated in the form of a 

 mesial fold, while, in true Pentamerus, the middle of the dorsal valve is de- 

 pressed, forming a dorsal sinus, with a corresponding elevation on the other or 

 ventral valve. 



Formation and Locality. Found very rarely in the Niagara rocks of the quarries east of the city 

 of Louisville, Ky. 



Genus Stricklandinia. Bmin gs . 



Stricklandia, Billings. Can. Nat. and Geol., Vol. 4 1859. 

 Etymology : Named in honor of Prof. Strickland. 



The name Stricklandia having been previously applied to a genus of fossil 

 plants, the author abandoned it and substituted Stricklandinia for it. This 

 genus includes such shells as Pentamerus lens, P. liratus, and P. laevis. They 

 differ from the real Pentamerus in having the valves usually sub -equal, and no 

 longitudinal septa or triangular chamber in the interior of the dorsal valve. 

 Both valves have an area, but in the dorsal it is usually linear, or slightly ex- 

 ceeding the thickness of the shell in height. The ventral valve has usually a 



